Roderick Hill, with Janie Brookshire, misses an opportunity to play a smarmy snake. Photo: Carol Rosegg

It’s tough going for a comedy like “Mary Broome,” which revolves around a spectacularly unsympathetic lead character. It’s not Mary herself, by the way — because this 1911 play really is about her lover, Leonard Timbrell. And he’s one big jerk.

The Mint Theater specializes in rescuing forgotten works from the dustbin, and it has its work cut out with Allan Monkhouse’s tricky piece. The result is an interesting curio, though maybe not a good one.

Unlike the uppity clan in “Downton Abbey,” which looks down on any cousin who works for a living, Monkhouse’s well-off Timbrell family associates money with industry.

But Leonard (Roderick Hill), the youngest son, happily remains idle. He claims to have a literary bent without doing much about it, and doesn’t practice the law for which he trained. He’s such a useless toff that Leonard’s father, Edward (Graeme Malcolm), actually pays him not to get involved in business.

Stranger still, the patriarch promises his wastrel a yearly allowance if he marries Mary Broome (Janie Brookshire), the housemaid he impregnated.

This is quite a departure from most upstairs/downstairs affairs, which usually end with the servant being fired or the baby being given up for adoption. Here, Mary keeps the baby and the guy, at least at first. And Edward’s gesture is less about generosity and more about how much he wants to be rid of his son.

The whole brouhaha is presented in the insouciant tone of a drawing-room comedy, with put-downs barely hidden behind bon mots. “I think I like you enough to marry you,” Leonard snidely tells Mary. Gee, thanks.

Monkhouse wrote Mary as something of a cipher, and Brookshire’s underplaying doesn’t help. Even when she makes a big decision at the end of the four acts — which speed by under two hours — she comes across as passive. When tragedy strikes (offstage), it barely registers.

Almost by default, Leonard comes to dominate the show, which isn’t such a good thing.

Is he a witty dilettante rebelling against his conventional family, or a condescending, selfish snake? Hill’s charmless performance tilts the scale toward the second option, leaving the rich ambiguities in Monkhouse’s writing largely unexplored. Too bad — the Mint missed a rare opportunity to make us fall for a bastard.